The invention relates to an improvement in a method and apparatus for controlling the drive of a centrifuge drum, and more particularly to controlling the differential speed at which the screw conveyor and the drum of a worm centrifuge are driven.
A feature of the invention is the measurement of the torque input to the screw conveyor and controlling the flow of hydraulic fluid to the motors for the screw conveyor and worm centrifuge inversely by increasing the flow to the motor drive for the screw conveyor when the torque input is increased. The motors are driven by a constant output pump and the total output of the pump is constantly utilized.
In German OS No. 25 51 789 there is disclosed a solid bowl worm centrifuge wherein hydraulic motors are used to drive the conveyor screw and to drive the centrifuge drum. These hydraulic motors are connected to three pump units by pressure lines and the pump units are driven by a drive motor. The control of the speed differential between the centrifuge drum and the screw conveyor is obtained dependent on the torque of the screw conveyor and/or of the centrifuge drum by modifying or controlling the quantities of hydraulic fluid supplied to the hydraulic motors. The quantities are controlled by the use of control valves arranged in pressure lines from the pumps to the motors.
In accordance with this type of structure, all three pumps must be constantly in operation for controlling the speed differential between the centrifuge drum and the screw conveyor. This occurs even when only a part of the quantities of hydraulic fluid supplied by the pumps is required for the drive of the centrifuge and for maintaining the speed differential between the centrifuge drum and the screw conveyor. As a result of this structure and operation, it is a mandatory consequence that part of the quantities of hydraulic fluid conveyed by the pumps must be constantly conducted back into a pressure vessel and the energy is thereby lost for the drive of the worm centrifuge. This represents a relatively high energy loss which must be delivered by the drive motor of the pumps.
This known control of the speed differential between the centrifugal drum and the screw conveyor not only requires a high output for the pump units, for the pressure lines and other connections, but also involves high operating costs due to the energy losses. Further, the drive motor for the pumps must be designed appropriately powerful enough and must be designed beyond the power required for normal operation of the centrifuge, and therefore must be over dimensioned.
An object of the invention is to provide a method and structure which avoids the aforementioned disadvantages and operates at optimum load distribution to the screw conveyor and to the centrifuge drum and permits an infinitely variable and practially energy-free loss control of the speed differential between the drum and the screw in an improved and simplfied manner.
The foregoing objective is achieved by a unique process and apparatus wherein with increasing torque required to drive the screw conveyor, such as caused by increase in load or input to the centrifuge, the quantity of hydraulic fluid supplied to the hydraulic motor of the screw conveyor is increased via control valves. This increase is uniquely matched by a decrease in quantity of hydraulic fluid delivered to the hydraulic motor of the centrifuge drum. Similarly, the same proportional or ratio is maintained with decrease in torque required to drive the screw conveyor. That is, as the torque decreases, the amount of hydraulic fluid supplied to the hydraulic motor of the screw conveyor is decreased and accordingly the hydraulic fluid delivered to the hydraulic motor of the centrifuge drum is proportionately increased. Because of this method and the results of the apparatus provided, the energy exerted by the drive motor for the pump, and supplied to the hydraulic motors from the pump, can be fully exploited for maintaining the oepration of the worm centrifuge at a satisfactory level and for controlling the speed differential between the centrifugal drum and the screw conveyor.
In accordance with the invention, the drive of the drum and of the screw conveyor can be accomplished with an appreciable reduced energy outlay compared to previously known drive arrangements for worm centrifuges. This reduced energy outlay provides the advantage that the drive motor and conveying pump can be designed as smaller units and designed and constructed for operation at optimum efficiency thereby obtaining an appreciable reduction in energy requirement and an appreciable reduction in initial construction costs or cost of purchase to the plant in which the machinery is used.
In accordance with the principles of the invention, the sum of the quantities of hydraulic fluid supplied to the hydraulic motors is held constant. This is particularly expedient when the suspension to be dewatered by the centrifugal separator is a suspension having an essentially constant solid/fluid mixture.
Other objects, advantages and features will become more apparent with the teaching of the principles of the present invention in connection with the disclosure of the preferred embodiment in the specification, claims and drawings, in which: